Electrode structure and method of manufacture



y 1946- H. B. LAW

ELECTRODE STRUCTURE AND METHOD OF MANUFACTURE Filed Oct. 25, 1942INVENTOR 5 l RNEY Patented July 2,' l946 ELECTRODE STRUCTURE AND METHODOE MANUFACTURE Harold B. Law, Princeton, N. J assignor to RadioCorporation of America, a corporation of Delaware Application October23, 1942, Serial No. 463,065

7 Claims.- (Cl. 49-79) My invention relates to television transmittintubes and electrode structures and more particularly to methods ofmanufacturing target structures suitable for use n tubes of the lowvelocity electron beam scanning and electron image types.

-In television transmitting tubes utilizing electron beam scanning withoptical or electrical imageproiection on a surface other than thesurface scanned by the electron beam, it has been proposed to utilize animage grid mosaic-type target, such as disclosed by Iams in his U. S.Patent No. 2,213,179. Such target electrode usually have a wire meshfoundation and are exceedingly difficult toconstruct, the task offorming a struc ture having over 100,000 electrically discrete highlyinsulated metal plugs extending through the target and insulated fromthe signal screen embedded in the target being a tedious and difficultmanufacturing problem. In addition, such electrodes, even thoughprepared with exceptional care, produce a spurious signal notrepresentative of the electron or of the optical image due to electricalor mechanical non-uniformities over the target surface. Suchu'niformities are accentuated when the electrode is used in electronbeam seaming tubes utilizing low velocity electron beams.

It is an object of my invention to provide tarprovide apertures throughtheiorindation opposite the depressions or bubble sections about or inwhich I provide a mosaic which may b photosensitive or'secondaryelectron emissive.

These and other objects, features, and advantages of my invention willbe apparentfrom the followin description and with reference to the.

accompanying drawing wherein:

9 Figures 1 through 6 are sectioned views of a target structurefollowing'six successive steps of manufacture.

It will be appreciated that the target structure made in accordance withmy invention i useful in many types of television transmitting tubes,and consequently, I have not shown in the drawing any particular type oftube to which it i ap-.

plicable. For example, the target structure may be utilized in imagetubes scanned by alow velocity electron beam such as described by Iamsin his U. S. Patent 2,213,179, although one modiflcation thereof may beutilized as a double-sided et structures for electron beam tubes such asof the television transmitting type producing higher sensitivity andlower distortion than structures constructed heretofore, as well as amethod whereby such structures may be manufactured with ease and at lowcost. It is another object to provide a target without an electricallyconductive foundation to which leakage may occur. It is a further objectof my invention to provide methods of manufacturing televisiontransmitting tube targets suitable for use for low velocity.electronbeam scanning which are capable of exceptionally high sensitivity withsubstantial elimination of all spurious signals. It i a still furtherobject to provide a tube having a target structure which may bemanufactured with-high uniformity and with ease and at low cost.

In accordance with my invention! rovide a thin sheet of insulatingmaterial preferably of vitreous construction and I develop a greatmultiplicity of very small depressions or bubbles in the foundation bycoating the foundation with a tacky or adhesive preferably volatilematerial. dismosaic electrode such as in a tube described by Iams in hisU. S. Patent 2,213,178. While the target electrodes of these tubes aresomewhat different, my method of manufacture provides electrodessuitable for such use.

Referring to Figure 1, the target foundation comprises a very thininitially imperforate foundation sheet I of electrically insulating orsemiinsulating material such a glass havinga resistance greater than 10ohm-centimeters. Preferably, an exceptionally thin homogeneous sheet ofvitreous material such as glass having the desired specific resistancedepending upon its specific use as referred to'hereinafter and beingsmooth and of uniform thickness may be used. I have used glass known inthe trade as Corning705 glass with satisfactory results. Preferably, thetarget foundation'sheet i has an initial thickness of from 0.001" to0.005". Such a thin sheet of vitreous material may be made by thecylinder proc- 1 cylinder longitudinally, and then opening out andtributing small particles or crystals of refractory 1 material over theadhesive and baking to provide asreat multiplicity of bubbles in thefoundation. Further in accordance with my invention I may flattening thesplit cylinder on a flattening stone in a flattening oven. Followingpreparation of the thin foundation sheet I and in accordance I with myinvention, I coat one surface of the sheet with a thin coating 3comprising a tackly, adhesive, and preferably volatile material whichdurdissolved in a solvent. ment known as Best-Test'as supplied by thev 31 small refractory particles as shown in Figure 2, the average size ofthe particles preferably being less than the thickness of the sheet I.These pardiflerent siz so that the results obtained with such variationin particle sizemay be differentiated. Following the application of thecoating 3 and the distribution of the particles 5 over its exposedsurface, I place the sheet I in aif'urnace.

or oven and heat the sheet to a temperature slightly exceeding itssoftening point. During the initial-stages of this hakingthe coating 3vaticles are preferably of uniform size and shape. 6 although I haveshown the particles 5 as being of be opened by this treatment as shownat the right in Figure 4. However, as is usually the case, if diflerentsized bubbles are formed as shown at the left of Figure 3, some bubblesmayinot be opened on the opposite side of the-sheet as shown at "the,left of Figure 4. .For, thedouble-sided mosaic structure, it isdesirable that as many as possible of the bubbles extend completelythrough the foundation sheet and I-then fill the apertures thusformed-with metal plugs 9 as shown in Fi ure 5. A suitable method offilling the apertures and forming the metal plugs is described by Rosein his U. S. Patent 2,175,701.,

porizes and as the'temperature isfurther raised i small bubbles ordepressions I-are formed-in thevitreous foundation sheet I as shown inFigure 3. I. have not been able to explain the-action upon heating thesheet bearingthe particles, but the 7 average size of thebubbles dependsupon the time of heating to a great extent.

The foundation as shown in the drawing may ;be etched to a greaterextentthan shown in Figure" 5 to assure the formation of the maximum Inumber of apertures. especially if the size of the I have obtained thebest results in practicing my invention by utilizing silicon carbideparticles,

Unio'n Rubber and Asbestos Company, of Trenton, N. J., is suitable forthis purpose. The rubber cement is applied and allowed to dry for a fewminutes and then the Carborundum particles grade. 600 are brushed overthe rubber coating.

particles 5 'is'non-unifo'rmas shown in Figure 3.. I have shown in Fi re6 a target foundation made in accordance with my invention particularlyadapted to tubes of the type described in the first-mentioned Iamspatent wherein the apertures I I of the sheet I are allowed to remainopen but are surrounded with small mosaic globules I3. The globules I3may be of silver and may be photosensitized as described by Iams tolimit the flow of electrons through the apertures II in accordance withcharges developedby an optical image formed on the globules It.Obviously, the globules I3 may be made photosensitive or secondaryelectron emissive by superficial- The rubber film being tacky does notmaterially I wet the Carborundum particles so that only a single layerof the particles sticks to the film.

The firing or baking operation is somewhat critical as to temperatureand time, although the bubbles begin to form around 775 C. for the 705glass. However, I prefer to place the prepared foundation in an ovenwhich has been heated previously to approximately 800 0., allowing thefoundation to remain in the oven for 5 minutes.

following which it is removed from the oven and cooled. Alternativelythe prepared foundation may be placed in a cold oven and the temperatureraised to 800 C., the foundation being allowed to remain for 2 to 5minutes after reaching this terns perature. The small Carborundumparticles are actually fused to the glass at this temperature.

Following the firing operation, I immerse the sheet in a hydrofluoricacid solution which dissolves the Carborundum particles as well as aportion of the glass foundation. Consequently, the

thickness of the original glass sheet is chosen to allow for this step.An aqueous solution of 10 parts water to 1 part concentratedhydrofiunric acid is preferred. The foundation then may be processedfurther depending upon the partionlar type: of tube for which the targetis designed, that is, whether of the double-sided mosaic type or of theperforated image type.

For providing a target of the double-sided type shown in Figure 5, Iprefer to provide perforations in the foundation sheet by opening .the

' bubbles to the opposite side of the sheet from that originally bearingthe particles 5. For example, the sheet may be immersed in thehydrofluoric acid to further reduce the thickness of the sheet, therebyopening the bubbles to form apertures 8 extending completely through thesheet. Pro- ,vide'd the bubbles were originally of substantially thesame size, substantially all of the bubbles will ly oxidizing theglobules and subjecting them to caesium or other alkali metal vapor.

Instead of distributing the refractory particles 5 over the entiresurface of the adhesive coated foundation they may be deposited as aregular array such as by settling the particles through, the intersticesof a wire mesh or otherwise apertured screen. This procedure allowsspaces between groups of bubbles which may be of advantage in certainapplications. Furthermore, substantially spherical bubbles may be formedby r moving the Carborundum particles following firingwithout the useof'acid. Thus the'partlcles may be removed by an abrasive action such asby rubbing the top surface of the foundation with fine emery paper. Ifthis method is followed, there will be substantially no rounding of thebubble openings and the bubbles will be substantially spherical. I

I claim:

1. The method of manufacturing a foundation for an electrode structurecomprising heating a vitreous insulating sheet bearing fine particles ofa refractory material at a temperature suficient to form bubbles in saidsheet underlying the said particles of refractory material and removingsaid particles from said sheet.-

v2. The method of manufacturing a foundation for an electrode structurecomprising coating a tsheet of glass with an adhesive, distributing oversaid adhesive small particles of a refractory material, heating saidsheet bearingsaid particles to a temperature sufiicient to cause theformation of bubbles in said sheet underlying said particles andremoving said particles to expose said bubbles.'

3. The method of manufacturing a foundation for an electrode structurecomprising the steps of coating a thin sheet of glass with small parti-4 acoaaaa said particles to expose said bubbles to the atmosphere.

4. The method of manufacturing a foundation A structure for a mosaicelectrode comprising forming a thin sheet of vitreous material, forminga tacky adhesive coating on one side of said sheet, affixing smallsilicon carbide particles to said coating, the size of said particlesbeing less than the thickness of said thin sheet, heating said coatedsheet and particles for a period of time suflicient to form bubbles onsaidsheet under said particles and removing said particles from saidsheet.

5. The method of manufacturing a mosaic electrode foundation comprisingthe steps of forming a thin sheet of glass between one thousandth andfive thousandths inches in thickness, coating said sheet of glass with avolatile rubber base adhesive, distributing particles of silicon carbideover the surface of said adhesive, heating said glass bearing saidparticles to a temperature at which said glass softens and developsbubbles underly- 6 6. The method of manufacturing a mosaic electrodefoundation comprising forming a thin sheet of glass having a softeningpoint below 800 C.,

, electrode foundation comprising forming a thin ing said particles,cooling said sheet and immersing said sheet in an acid which is capableof dissolving said particles to remove said particles from said sheetleaving said bubbles exposed on one surface thereof.

sheet of glass of from one thousandth to five thousandths inch inthickness, coating one surface of said glass sheet with a rubbercontaining adhesive, forming a layer of silicon carbide particles havingan average size less than the thickness of said sheet on said adhesive,heating said sheet of glass to a temperature above 775 C. for a timesuflicient to form bubbles under the said particles, cooling said sheetand removing said particles to expose said bubbles.

HAROLD B. LAW.

